1. Field of the Invention
The present invention relates generally to a storage system for use with a computer system, and relates more particularly to a storage system having multiple types of input/output interfaces.
2. Description of Related Art
There are two general types of interfaces (“I/F” below) used in computer systems to connect storage devices to the computer. The first type is the block I/O interface, which uses the data management unit of the storage device, the data block, as the unit for input/output (“I/O” below) access. The block I/O interface includes a fibre channel, SCSI (small computer systems interface), or other interface. The second type is the file I/O interface, which uses file units for I/O access. The file I/O interface is used with the network file system (NFS), common Internet file system (CIFS), and other file systems that use data from storage devices managed by a file server connected via a network.
Techniques for interconnecting a plurality of storage devices via a network can also be grouped in two categories based on the differences in the interfaces described above. The first is a Storage Area Network (SAN), a network for connecting to storage devices by connecting computers and storage devices using a fibre channel. The second is a Network-Attached Storage (NAS), a method for accessing storage devices with the file I/O interface by connecting the storage devices to a local area network (LAN) such as commonly used for communication between computers.
The SAN uses a high speed network that is dedicated to storage and is separate from the network used for sending messages between computers. Compared with NAS systems having the storage devices connected via a LAN, SAN systems enable faster data transfers. Protocol overhead is also small and fast response can be achieved with SAN systems because the block I/O interface is used. The disadvantage to SAN systems is that setup costs are high because a dedicated network is required. SAN is therefore used primarily in the backbone system of corporate computer networks, frequently for database applications.
With NAS the storage system is connected directly to the LAN. Setup costs are low and setup is relatively easy because an existing LAN can be used. A standardized NFS, CIFS, or other network file system is also used for the interface, and data is managed in file units. Data management is therefore easy, and files can be easily shared between plural computers. The disadvantage to NAS is that because the storage system is accessed via the same LAN used for communication between computers, LAN traffic (load) is increased. The processing overhead of a network file system is also high, and response is slower than with block I/O. For these reasons NAS is used primarily for corporate file management systems, Web content management, CAD data file management, and other such applications.
As will be known from the above, NAS and SAN are mutually complementary and are used for different purposes. NAS and SAN are therefore generally used for appropriate applications.
Technology for combining SAN and NAS is also known from the prior art as described below.
A computer is connected to a storage system through a file server connected to a LAN, or the computer and file server are connected directly to the storage system via a SAN. The file server is connected to the storage system through a fibre channel or other interface. The storage system used in this case is typically a disk array system having a plurality of disk drive units and a disk controller located between the plural disk drive units and the computers for controlling data access to the disk drive units.
To access data stored on the storage system, a computer connected only to the file server accesses files in the storage system via the file server using the NFS, CIFS, or other protocol. Computers connected to both the file server and SAN must send a request to the file server in order to access the storage system, but data is transferred from the storage system to the computer directly over the SAN.
It will be noted that with this prior art method a NAS system is created by the file server and the storage system connected to the file server by a fibre channel. In other words, this prior art technology creates a NAS system above the SAN.